Enhanced Light Extraction from p‑Si Nanowires/n-IGZO Heterojunction LED by Using Oxide–Metal–Oxide Structured Transparent Electrodes

Heterojunction light-emitting diodes (LEDs) comprising p-type Si nanowires (p-Si NWs) and n-type indium gallium zinc oxide (n-IGZO) were fabricated with the different top electrode materials: Al, indium zinc oxide (IZO), and IZO/Ag/IZO oxide–metal–oxide (OMO) multilayer. All the LEDs exhibited typical rectifying behaviors of the p–n junction. Moreover, broad light-emission spectra in the visible range were observed because of the quantum confinement effect (QCE) of the Si NW and Si nanocrystals/nonstoichiometric Si oxide (SiO_<i>x</i>) (<i>x</i> < 2) interfaces. In comparison to the LEDs with Al and single IZO electrode, the LED with the OMO multilayer electrode exhibited an enhanced optical performance because the OMO multilayer had an excellent transmittance of 87.7% in the visible range with a low sheet resistance of 5.65 Ω/sq. Furthermore, by investigating the transmittance spectra of the single IZO and OMO multilayer electrodes as a function of the light incidence angle, the OMO multilayer electrode is confirmed to be more suitable for white light emission from p-Si NWs/n-IGZO heterojunction LED

Effect of Nonionic Surfactant Additive in PEDOT:PSS on PFO Emission Layer in Organic–Inorganic Hybrid Light-Emitting Diode

Poly­(9,9-dioctylfluorene) (PFO) has attracted significant interests owing to its versatility in electronic devices. However, changes in its optical properties caused by its various phases and the formation of oxidation defects limit the application of PFO in light-emitting diodes (LEDs). We investigated the effects of the addition of Triton X-100 (hereinafter shortened as TX) in poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) to induce interlayer diffusion between PEDOT:PSS and PFO to enhance the stability of the PFO phase and suppress its oxidation. Photoluminescence (PL) measurement on PFO/TX-mixed PEDOT:PSS layers revealed that, upon increasing the concentration of TX in the PEDOT:PSS layer, the β phase of PFO could be suppressed in favor of the glassy phase and the wide PL emission centered at 535 nm caused by ketone defects formed by oxidation was decreased considerably. LEDs were then fabricated using PFO as an emission layer, TX-mixed PEDOT:PSS as hole-transport layer, and zinc oxide (ZnO) nanorods as electron-transport layer. As the TX concentration reached 3 wt %, the devices exhibited dramatic increases in current densities, which were attributed to the enhanced hole injection due to TX addition, along with a shift in the dominant emission wavelength from a green electroluminescence (EL) emission centered at 518 nm to a blue EL emission centered at 448 nm. The addition of TX in PEDOT:PSS induced a better hole injection in the PFO layer, and through interlayer diffusion, stabilized the glassy phase of PFO and limited the formation of oxidation defects

High-Performance Green Light-Emitting Diodes Based on MAPbBr₃–Polymer Composite Films Prepared by Gas-Assisted Crystallization

The morphology of perovskite films has a significant impact on luminous characteristics of perovskite light-emitting diodes (PeLEDs). To obtain a highly uniform methylammonium lead tribromide (MAPbBr₃) film, a gas-assisted crystallization method is introduced with a mixed solution of MAPbBr₃ precursor and polymer matrix. The ultrafast evaporation of the solvent causes a high degree of supersaturation which expedites the generation of a large number of nuclei to form a MAPbBr₃–polymer composite film with full surface coverage and nano-sized grains. The addition of the polymer matrix significantly affects the optical properties and morphology of MAPbBr₃ films. The PeLED made of the MAPbBr₃–polymer composite film exhibits an outstanding device performance of a maximum luminance of 6800 cd·m^–2 and a maximum current efficiency of 1.12 cd·A^–1. Furthermore, 1 cm² area pixel of PeLED displays full coverage of a strong green electroluminescence, implying that the high-quality perovskite film can be useful for large-area applications in perovskite-based optoelectronic devices

Low-Temperature Facile Synthesis of Sb-Doped p‑Type ZnO Nanodisks and Its Application in Homojunction Light-Emitting Diode

This study explores low-temperature solution-process-based seed-layer-free ZnO p–n homojunction light-emitting diode (LED). In order to obtain p-type ZnO nanodisks (NDs), antimony (Sb) was doped into ZnO by using a facile chemical route at 120 °C. The X-ray photoelectron spectra indicated the presence of (Sb_Zn–2V_Zn) acceptor complex in the Sb-doped ZnO NDs. Using these NDs as freestanding templates, undoped n-type ZnO nanorods (NRs) were epitaxially grown at 95 °C to form ZnO p–n homojunction. The homojunction with a turn-on voltage of 2.5 V was found to be significantly stable up to 100 s under a constant voltage stress of 5 V. A strong orange-red emission was observed by the naked eye under a forward bias of 5 V. The electroluminescence spectra revealed three major peaks at 400, 612, and 742 nm which were attributed to the transitions from Zn_i to VBM, from Zn_i to O_i, and from V_O to VBM, respectively. The presence of these deep-level defects was confirmed by the photoluminescence of ZnO NRs. This study paves the way for future applications of ZnO homojunction LEDs using low-temperature and low-cost solution processes with the controlled use of native defects

Enhanced Light Stability of InGaZnO Thin-Film Transistors by Atomic-Layer-Deposited Y₂O₃ with Ozone

We report the effect of Y₂O₃ passivation by atomic layer deposition (ALD) using various oxidants, such as H₂O, O₂ plasma, and O₃, on In–Ga–Zn–O thin-film transistors (IGZO TFTs). A large negative shift in the threshold voltage (<i>V</i>_th) was observed in the case of the TFT subjected to the H₂O-ALD Y₂O₃ process; this shift was caused by a donor effect of negatively charged chemisorbed H₂O molecules. In addition, degradation of the IGZO TFT device performance after the O₂ plasma-ALD Y₂O₃ process (field-effect mobility (μ) = 8.7 cm²/(V·s), subthreshold swing (SS) = 0.77 V/dec, and <i>V</i>_th = 3.7 V) was observed, which was attributed to plasma damage on the IGZO surface adversely affecting the stability of the TFT under light illumination. In contrast, the O₃-ALD Y₂O₃ process led to enhanced device stability under light illumination (Δ<i>V</i>_th = −1 V after 3 h of illumination) by passivating the subgap defect states in the IGZO surface region. In addition, TFTs with a thicker IGZO film (55 nm, which was the optimum thickness under the current investigation) showed more stable device performance than TFTs with a thinner IGZO film (30 nm) (Δ<i>V</i>_th = −0.4 V after 3 h of light illumination) by triggering the recombination of holes diffusing from the IGZO surface to the insulator–channel interface. Therefore, we envisioned that the O₃-ALD Y₂O₃ passivation layer suggested in this paper can improve the photostability of TFTs under light illumination